The present invention generally relates to pendulous compensators and, more particularly, to a system for dampening vibrations, and especially low velocity vibratory motion, of a pendulous compensator.
Laser beam systems have been employed in numerous surveying and construction applications. For instance, laser beam projectors are available which will generate a horizontal reference beam. In order to ensure that the reference laser beam emanating from a vertically-oriented laser source in the projector will continue to point in the desired horizontal direction even if the laser source becomes tilted from a true vertical orientation, it is possible to employ a pendulous compensator in the projector.
A simplified schematical diagram of a conventional laser beam projector 10 is shown in FIG. 1 herein. Basically, the projector 10 includes a casing 12, a laser beam source 14, expander lenses 16 and a pendulous compensator 18. The pendulous compensator 18 has a mounting bracket 20, a cantilever beam 22 mounted to and suspended downwardly from the bracket 20 for movement relative thereto within a plane parallel to the plane of the drawing and oriented orthogonal to the wider dimension of the beam 22, and a laser beam reflecting mirror 24 fixedly attached at a forty-five degree angle to the lower end of the cantilever beam 22. The laser source 14 and the mounting bracket 20 are fixedly attached to the casing 12 in such alignment that a laser beam 26 projected upward from the laser source 14 would pass through the attachment point A of the cantilever beam 22 on the mounting bracket 20 if the cantilever beam 22 and mirror 24 were removed and also would pass through the bending plane of the cantilever beam 22.
Therefore, when the projector 10 is placed in a true vertical orientation, the cantilever beam 22, which due to gravity always assumes a true vertical orientation, extends in alignment with the laser beam 26 being projected vertically upward from the laser source 14. The laser beam 26 first passes through the expander lenses 16 which expand and then collimate the beam before it reaches the mirror 24. The mirror 24, oriented at forty-five degrees to the vertical, then reflects the beam 26 in the desired horizontal direction within the pivotal plane of the cantilever beam 22.
Even if the laser beam projector 10 becomes slightly tilted away from the vertical, it is desired that the laser beam continue to deflect in the horizontal direction. The pendulous compensator 18 operates to ensure such result. As seen in an exaggerated form in FIG. 2, the casing 12 and thus the laser beam 26 as it emerges from the laser source 14 are oriented at an angle relative to the vertical. However, the cantilever beam 22 of the pendulous compensator 18, which due to the effect of gravity always bends toward a true vertical orientation, is now displaced counterclockwise about its mounting point A from the line of the emergent laser beam 26 through one-half the angle of tilt which exactly compensates for the angular tilt of the casing 12. In accordance with known principles of geometry and optics, the laser beam 26 then continues to be reflected in the desired horizontal direction.
The compensatory operation of a pendulous compensator as just described is satisfactory under conditions where it is not subject to vibrations. However, errors arise from oscillation of the cantilever beam due to vibrations which commonly occur in surveying and construction environments. Pneumatic and eddy current damping arrangements have been used in the past in an attempt to nullify the effects of vibrations, but both arrangements have their drawbacks. Pneumatic damping arrangements are somewhat difficult to adjust to provide the correct amount of damping. Oftentimes, over or under dampening of the pendulous compensator results. Eddy current dampening arrangements have not proven to be very useful for low velocity damping.
Consequently, in view of the shortcomings of the above-mentioned prior art dampening arrangements, there is still a need for a technique to overcome the deleterious effects of vibrations on pendulous compensators.